1. Field of the Invention
This invention relates to a so called spinal joint.
2. Description of the Related Art
During spinal surgery in the human spine, certain fixation apparatuses are used to accomplish a displacement and subsequent fixation of vertebrae relative to each other.
The fixation apparatuses used for such and similar purposes comprise two or more body members, each of which being securable to a vertebra or bone by means of so called bone screws, and connected to each other by means of screw spindles or other rigid connection members which have the capability of changing their length. In this manner the body members may be displaced by manipulating the screw spindles or the like. The setting is secured, for instance, by blocking the rotation of the screw spindle. It will however be noted that in fixation apparatuses with more than two such body members it is usually only necessary to displace those vertebrae which are connected to the outermost body members while the vertebrae therebetween will not be displaced. In such cases, no displacement of the vertebrae connected to those body members will take place.
The body members usually are in the shape of two blocks. One block supports at least one bone screw, and the other block forms a guide for the screw spindle. These blocks are so connected to each other that they may be turned a certain angle relative to each other and then locked in the desired mutual angular position.
In the following such a body member will be called a spinal joint.